Fix import JWT payload

Background

We are preparing for Phase 2 of the Container Registry migration which involves importing all existing container repositories to the new platform (Phase 1 involved routing all new container repositories to the new platform). See &7316 (closed) for full details of how the import will work.

The registry will make requests to import container repositories so in !78489 (merged) we added a new token scope for import access. Unfortunately, the payload of that token was implemented incorrectly.

What does this MR do and why?

This MR updates the payload of the JWT for import access to use a registry type and grant * actions.

It is safe to update the method signature because this method is not yet used anywhere.

I am considering this typemaintenance rather than bug since the method was introduced in the same milestone as this MR (%14.8).

Screenshots or screen recordings

Before: Token was granted on a per-repository basis:

[1] pry(main)> token = Auth::ContainerRegistryAuthenticationService.import_access_token('gitlab-org/gitlab-test')
[2] pry(main)> JWT.decode(token, nil, false)
=> [{"access"=>[{"type"=>"repository", "name"=>"gitlab-org/gitlab-test", "actions"=>["import"]}], ....]

After: Token is granted for the registry:

[5] pry(main)> token = Auth::ContainerRegistryAuthenticationService.import_access_token
[6] pry(main)> JWT.decode(token, nil, false)
=> [{"access"=>[{"type"=>"registry", "name"=>"import", "actions"=>["*"]}], ...]

How to set up and validate locally

In the rails console:

token = Auth::ContainerRegistryAuthenticationService.import_access_token
JWT.decode(token, nil, false)

You should see:

• type: "registry"
• name: "import"
• actions: ["*"]

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #349743 (closed), #351587 (closed)